This disclosure relates to borehole tools and apparatus, such as those used in drilling oil and gas wells. More particularly, it relates to drilling jars and to methods and apparatus for providing a mechanical lock that prevents a drilling jar from actuating. More particularly, the embodiments described herein provide a lock that is integrated into the drilling jar and that automatically locks and unlocks.
Jars are mechanical devices used downhole in a wellbore to deliver an impact load to the drilling string or to another downhole component, especially when that component is stuck. Jars may be designed for drilling or fishing applications, are generally available as hydraulically or mechanically actuated, and can be designed to strike upward, downward, or both. While their respective designs can be quite different, their operation is similar in that energy stored in the drillstring is suddenly released when the jar is actuated, known as tripping or firing.
In the case of “jarring up” at a location above a bottomhole assembly (BHA) that is stuck, the driller slowly pulls up on the drillstring but the BHA, because it is stuck, does not move. Since the top of the drillstring is moving up, the drillstring itself is stretching and storing energy. When the jar fires, one section of the jar is allowed to suddenly move axially relative to a second until the moving section impacts a steel shoulder formed on the stationary section of the jar, thereby imparting an impact load on the drillstring.
Many jar designs include a tripping or firing mechanism that prevents the jar from operating until the desired tension is applied to the string. Such jars are designed to be reset by simple drill string manipulation, and are thus capable of repeated operation, or firing, before being recovered from the well.
Before a jar is run into a well, while the jar is being stored on the drill floor, or after it is retrieved, it is often desirable to have a mechanism available to lock the jar into an open position to prevent unintentional firing, which can cause injury to personnel on the rig floor. Keeping the tool locked in the open position can also prevent accidental loss of the tool string downhole or damage to rig, which might result from the unintentional firing of the tool. Current solutions to this problem include the use of an internal mechanical latch and/or an external safety collar.
The conventional mechanical latch is set to release at a specific load in order to prevent unintentional firing while running the drilling assembly tripping into or out of the hole, i.e. tripping. When the predetermined latch release load is applied to the jar, the latch releases and the jar can be used as desired. One drawback of many of these internal latches is that every time the tool is stroked back, or reset, to the initial position, the latch is re-engaged. In order to release the latch, the release load must again be applied to the jar, creating additional steps in the procedure used to fire the jar. Another drawback of many mechanical latch designs is that, since the latch is designed to unlatch at a specified load, if the load is exceeded unintentionally, such as by the jar being handled improperly on the rig floor, the jar is configured to stroke and/or fire.
The typical external safety collar, also known as a “dog collar,” consists of a two-piece sleeve with a lock that attaches to an exposed portion of the jar and keeps the tool from closing. The collar is designed to support any possible amount of weight above the jar as well that may be applied during storage on the rig floor. These external safety collars generally work as intended, and are currently being utilized in the field, but there are problems associated with their use.
Due to the rigors of use and possible mishandling, the external safety collars may get damaged and/or worn, possibly causing the safety collar to not fully latch. This damage may make the collar difficult to install on the tool or can potentially cause the collar to unlatch and fall from the tool. On a drilling rig, the collar may be stored well above the rig floor, such as a height of approximately 30 ft to 90 ft above the rig floor. Obviously, a heavy collar falling from this height puts the personnel and equipment on the rig floor at risk. Recognizing this risk, some drilling companies are requiring a backup safety strap be added to the safety collars, insuring that the collar cannot fall off accidentally. Unfortunately, securing an additional safety strap increases the time needed to secure the tool.
Another drawback to the external safety collar is that the collar must be installed on the jar each time that it is pulled from the hole, and then must be removed before the tool is run again. Therefore, the collar is another piece of separate drilling equipment that must be maintained and stored on the rig. There is also a risk that rig floor personnel may forget to remove the safety collar before running the tool into the well. Running the jar with the safety collar installed will prevent operation of the jar and can cause the jar to get stuck in the hole, necessitating a costly procedure to extricate the stuck tool.
Therefore, the embodiments of the present invention are directed to methods and apparatus for providing for a positive lock mechanism for a drilling jar that seeks to overcome certain of the limitations or drawbacks of the prior art.